The mechanisms by which mutations in BRCA1 result in increased risk of breast cancer are not yet fully understood, but are thought to revolve around deficits in cellular machinery responsible for the maintenance of DNA integrity, including DNA repair functions. In addition to well-known effects on repair of double-strand breaks, mutations in BRCA1 are now recognized to impact multiple processes involved in maintaining DNA integrity. Emerging evidence indicates that psychological stress can also negatively impact DNA integrity through molecular pathways leading to increased ROS levels, as well as reductions in DNA repair capacity. These considerations suggest the central hypothesis of our planned program of research: women with BRCA1 mutations may be particularly susceptible to negative effects of psychological stress on DNA integrity. As a first critical test of that hypothesis we will explore the relationships between psychological stress and DNA damage in two conceptually and logistically interrelated pilot studies (final n=50; 25 BRCA1+, 25 age-, race-matched BRCA1-) to confirm feasibility and explore effect sizes for hypothesized relationships. The first pilot study (Aim 1) will use a cross-sectional correlational study design with one primary outcome: baseline DNA damage levels in peripheral blood mononuclear cells (PBMCs) assessed using an innovative CometChip technology under alkaline conditions, (with damage secondarily characterized by assay of: ?-H2AX, pATM, and DNA 8-OHdG). Statistical analyses will explore the strength of relationships between DNA damage levels and participants' responses on validated measures of psychological stress and related constructs, as well as the contribution of DNA repair capacity assessed by recovery from damage induced by ex vivo gamma radiation. The second pilot study (Aim 2) will use an experimental study design with a primary outcome of DNA damage levels in PBMCs isolated from blood samples collected: before (Baseline, T1), immediately after (Stress, T2), and 75 minutes after (Recovery, T3) exposure of participants to the Trier Social Stress Test (TSST), the most well validated experimental stress paradigm in the psychobiological literature. The concurrent use of both research designs with the same study sample and shared blood samples (Baseline) provides a cost effective way to test our overarching hypothesis with approaches having high internal validity (experimental study) and strong external validity (association study), while also allowing direct comparisons between the results from the two approaches. Aim 1: To statistically examine the relationships between psychological stress levels and DNA damage levels in women with (BRCA1+ Group) and without (BRCA1- Group) BRCA1 mutations. Aim 2: To experimentally investigate the impact of acute psychological stress on levels of DNA damage in women with and without BRCA1 mutations. This R03-supported pilot work will document feasibility and provide effect sizes for study hypotheses that will be used as preliminary data for a comprehensive R01 application. Results have methodological, theoretical, and public health significance for reducing breast cancer risk in BRCA1+ women.